Sailing is the propulsion of a vehicle and the control of its movement with large (usually fabric) foils called sails. By changing the rigging, rudder, and sometimes the keel or center board, a sailor manages the force of the wind on the sails in order to move the vessel relative to its surrounding medium (typically water, but also land and ice) and change its direction and speed.
Sails on sailboats act as air foils and utilize the wind and force created on the foil to provide forward force for the boat. The force resultant from the sail is based on a number of factors including the speed of the wind, the aerodynamic shape of the sail (foil), and the angle of the sail or foil relative to the wind. Trained sailors with experience understand the balance of these variables. Through manipulation of these variables they attempt to produce the optimal forward force on the boat, which is not readily known to the sailor. Only by gleaning information on how the boat feels, position of simple telltales, or gauging by the relative speed of the boat does the sailor know to adjust the sail setup. The novice attempts to set the sail, but only by guess due to the lack of any performance indication. This provides a barrier to entry for the untrained boater, who would shy away from the experience due to lack of skill.